Photoelectric conversion element, solid-state imaging device, and electronic apparatus

ABSTRACT

A photoelectric conversion element according to an embodiment of the disclosure includes a first electrode and a second electrode, and an organic semiconductor layer. The first electrode and the second electrode are disposed to face each other. The organic semiconductor layer is provided between the first electrode and the second electrode, and contains a fullerene derivative modified by a substituent having an absorbance smaller than that of a fullerene.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/574,592, filed Nov. 16, 2017, which is a U.S.National Phase of International Patent Application No. PCT/JP2016/064884filed on May 19, 2016, which claims priority benefit of Japanese PatentApplication No. JP 2015-108832 filed in the Japan Patent Office on May28, 2015. Each of the above-referenced applications is herebyincorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to, for example, a photoelectric conversionelement using an organic semiconductor, a solid-state imaging deviceprovided with the photoelectric conversion element, and an electronicapparatus.

BACKGROUND ART

In recent years, there has been progress in miniaturization of a pixelsize in a solid-state imaging device such as a charge coupled device(CCD) image sensor and a complementary metal oxide semiconductor (CMOS)image sensor. This leads to a decrease in the number of photons thatenter a unit pixel, thus leading to lowered sensitivity as well as alowered S/N ratio. Further, in a case of using a color filter in whichprimary color filters of red, green, and blue are two-dimensionallyarrayed for colorization, pieces of light of green and blue are absorbedby the color filter in a red pixel, thus causing the sensitivity to belowered. Furthermore, an interpolation process is performed betweenpixels upon generation of each color signal, thus causing occurrence ofa so-called false color.

Accordingly, for example, PTL 1 discloses a solid-state imaging deviceincluding, in a single pixel, for example, an organic photoelectricconversion section that detects green light to generate a signalelectric charge in accordance with the detected green light, andphotodiodes (inorganic photoelectric conversion sections) that detectred light and blue light, respectively. The disclosed solid-stateimaging device thus obtains three color signals in the single pixel toimprove the lowered sensitivity.

Moreover, for the purpose of further improving a photoelectricconversion efficiency, for example, PTL 2 discloses a photoelectricconversion element using a fullerene or a fullerene derivative as ap-type semiconductor of a photoelectric conversion film configured bythe p-type semiconductor and an n-type semiconductor. PTL 3 discloses aphotoelectric conversion element using, as a photoelectric conversionlayer, an organic photoelectric conversion dye, a fullerene or afullerene derivative, and a fullerene polymer.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Application Publication No.    2003-332551-   PTL 2: Japanese Unexamined Patent Application Publication No.    2007-123707-   PTL 3: Japanese Unexamined Patent Application Publication No.    2011-199253

SUMMARY OF INVENTION

However, as in the above-described PTLs 2 and 3, in a case where thephotoelectric conversion layer itself has a spectroscopic function, whensimply using the fullerene or the fullerene derivative as thephotoelectric conversion layer, there is an issue of a deterioratedspectroscopic shape of the photoelectric conversion element due to abroad absorption spectrum of the fullerene, which leads to lowered colorreproducibility.

It is therefore desirable to provide a photoelectric conversion element,a solid-state imaging device, and an electronic apparatus that make itpossible to improve a photoelectric conversion efficiency of apredetermined wavelength region.

A photoelectric conversion element according to an embodiment of thedisclosure includes a first electrode and a second electrode, and anorganic semiconductor layer. The first electrode and the secondelectrode are disposed to face each other. The organic semiconductorlayer is provided between the first electrode and the second electrode,and contains a fullerene derivative modified by a substituent having anabsorbance smaller than that of a fullerene.

A solid-state imaging device according to an embodiment of thedisclosure is provided with pixels each having one or a plurality oforganic photoelectric conversion sections. The organic photoelectricconversion section includes a first electrode and a second electrode,and an organic semiconductor layer. The first electrode and the secondelectrode are disposed to face each other. The organic semiconductorlayer is provided between the first electrode and the second electrode,and contains a fullerene derivative modified by a substituent having anabsorbance smaller than that of a fullerene in a visible range.

An electronic apparatus of the disclosure includes the above-describedsolid-state imaging device according to the embodiment of thedisclosure.

According to the photoelectric conversion element, the solid-stateimaging device, and the electronic apparatus of the respectiveembodiments of the disclosure, the fullerene derivative modified by asubstituent having an absorbance smaller than that of a fullerene in avisible range is used as the semiconductor layer provided between thefirst electrode and the second electrode that are disposed to face eachother. Subjecting a fullerene to polysubstituted modification causes anabsorption wavelength peak to be shifted toward shorter wavelength side,and reduces an interaction between fullerenes. This improves thespectroscopic shape of the photoelectric conversion element using thefullerene.

According to the photoelectric conversion element, the solid-stateimaging device, and the electronic apparatus of the respectiveembodiments of the disclosure, the semiconductor layer provided betweenthe first electrode and the second electrode contains the fullerenederivative modified by a substituent having an absorbance smaller thanthat of a fullerene in a visible range. Accordingly, the absorptionwavelength peak of the fullerene is shifted toward shorter wavelengthside, and an interaction between fullerenes are reduced, thus improvingthe spectroscopic shape of the photoelectric conversion element usingthe fullerene. In other words, it becomes possible to enhance thephotoelectric conversion efficiency of the predetermined wavelengthregion. It is to be noted that the effects described here are notnecessarily limitative, and may be any of effects described in thedisclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an outline configuration of aphotoelectric conversion element according to an embodiment of thedisclosure.

FIG. 2 is plan view of a correlation among an organic photoelectricconversion layer, a protective film (upper electrode), and a contacthole in terms of position of formation thereof.

FIG. 3A is a cross-sectional view of a configuration example of aninorganic photoelectric conversion section.

FIG. 3B is another cross-sectional view of the inorganic photoelectricconversion section illustrated in FIG. 3A.

FIG. 4 is a cross-sectional view of a configuration (extraction ofelectrons on lower side) of an electric charge (electron) accumulationlayer of an organic photoelectric conversion section.

FIG. 5A is a cross-sectional view that describes a method ofmanufacturing the photoelectric conversion element illustrated in FIG.1.

FIG. 5B is a cross-sectional view of a step subsequent to FIG. 5A.

FIG. 6A is a cross-sectional view of a step subsequent to FIG. 5B.

FIG. 6B is a cross-sectional view of a step subsequent to FIG. 6A.

FIG. 7A is a cross-sectional view of a step subsequent to FIG. 6B.

FIG. 7B is a cross-sectional view of a step subsequent to FIG. 7A.

FIG. 7C is a cross-sectional view of a step subsequent to FIG. 7B.

FIG. 8 is an explanatory cross-sectional view of a main part thatdescribes a working of the photoelectric conversion element illustratedin FIG. 1.

FIG. 9 is a schematic diagram that describes the working of thephotoelectric conversion element illustrated in FIG. 1.

FIG. 10 illustrates ultraviolet visible absorption spectra of afullerene (C₆₀) and a fullerene derivative (C₆₀F₃₆).

FIG. 11 illustrates ultraviolet visible absorption spectra of fullerenederivatives.

FIG. 12 illustrates current-voltage characteristics of the organicphotoelectric conversion section of the present embodiment before andafter light irradiation.

FIG. 13 illustrates ultraviolet visible absorption spectra of theorganic photoelectric conversion layer of the present embodiment.

FIG. 14 is a functional block diagram of a solid-state imaging deviceusing, as a pixel, the photoelectric conversion element illustrated inFIG. 1.

FIG. 15 is a block diagram illustrating an outline configuration of anelectronic apparatus using the solid-state imaging device illustrated inFIG. 14.

MODES FOR CARRYING OUT THE INVENTION

In the following, some embodiments of the disclosure are described indetail with reference to drawings. It is to be noted that description isgiven in the following order.

1. Embodiment (An example in which fullerene having undergonepolysubstituted modification is used for organic photoelectricconversion section)

1-1. Basic Configuration 1-2. Manufacturing Method 1-3. Workings andEffects 2. Application Examples 1. Embodiment

FIG. 1 illustrates a cross-sectional configuration of a photoelectricconversion element (photoelectric conversion element 10) according to anembodiment of the disclosure. The photoelectric conversion element 10constitute a single pixel in, for example, a solid-state imaging device(described later) such as a CCD image sensor and a CMOS image sensor.The photoelectric conversion element 10 includes, on side of a frontsurface (surface S2 opposite to light-receiving surface) of asemiconductor substrate 11, pixel transistors (including transfertransistors Tr1 to Tr3 described later) formed as well as a multi-layerwiring layer (multi-layer wiring layer 51).

The photoelectric conversion element 10 of the present embodiment has astructure in which one organic photoelectric conversion section 11G andtwo inorganic photoelectric conversion sections 11B and 11R are stackedin a vertical direction. The organic photoelectric conversion section11G selectively detects pieces of light of different wavelength regionsto perform photoelectric conversion. The organic photoelectricconversion section 11G includes an organic semiconductor and a fullerenehaving undergone polysubstituted modification (fullerene derivative).

(1-1. Basic Configuration)

The photoelectric conversion element 10 has a stacked structure of oneorganic photoelectric conversion section 11G and two inorganicphotoelectric conversion sections 11B and 11R. This allows forobtainment of respective color signals of red (R), green (G), and blue(B) using a single element. The organic photoelectric conversion section11G is formed on a rear surface (surface S1) of the semiconductorsubstrate 11, and the inorganic photoelectric conversion sections 11Band 11R are formed to be embedded inside the semiconductor substrate 11.Description is given below of a configuration of each section.

(Organic Photoelectric Conversion Section 11G)

The organic photoelectric conversion section 11G is an organicphotoelectric conversion element that uses an organic semiconductor toabsorb light (green light in this example) of a selective wavelengthregion, thus generating an electron-hole pair. The organic photoelectricconversion section 11G has a configuration in which an organicphotoelectric conversion layer 17 is interposed between a pair ofelectrodes (lower electrode 15 a and upper electrode 18) that extract asignal electric charge. As described later, the lower electrode 15 a andthe upper electrode 18 are electrically coupled toelectrically-conductive plugs 120 a 1 and 120 b 1 each embedded insidethe semiconductor substrate 11, through a wiring layer and a contactmetal layer. It is to be noted that the organic photoelectric conversionlayer 17 of the present embodiment is a specific example of an “organicsemiconductor layer” in the disclosure.

Specifically, in the organic photoelectric conversion section 11G,interlayer insulating films 12 and 14 are formed on the surface S1 ofthe semiconductor substrate 11. The interlayer insulating film 12 hasthrough-holes provided in respective regions that face theelectrically-conductive plugs 120 a 1 and 120 b 1 described later.Electrically-conductive plugs 120 a 2 and 120 b 2 are embedded in therespective through-holes. The interlayer insulating film 14 has wiringlayers 13 a and 13 b embedded in respective regions that face theelectrically-conductive plugs 120 a 2 and 120 b 2. The lower electrode15 a and a wiring layer 15 b electrically separated from the lowerelectrode 15 a by the insulating film 16 are provided on the interlayerinsulating film 14. The organic photoelectric conversion layer 17 isformed on the lower electrode 15 a, among those, and the upper electrode18 is formed to cover the organic photoelectric conversion layer 17. Aprotective film 19 is formed on the upper electrode 18 to cover asurface of the upper electrode 18, although the detail is describedlater. A contact hole H is provided in a predetermined region of theprotective film 19, and a contact metal layer 20 is formed on theprotective film 19. The contact metal layer 20 fills the contact hole H,and extends up to a top surface of the wiring layer 15 b.

The electrically-conductive plug 120 a 2 functions as a connectortogether with the electrically-conductive plug 120 a 1, and forms atransmission path of an electric charge (electron) from the lowerelectrode 15 a to a green electricity storage layer 110G describedlater. The electrically-conductive plug 120 b 2 functions as a connectortogether with the electrically-conductive plug 120 b 1, and forms adischarge path of an electric charge (hole) from the upper electrode 18together with the electrically-conductive plug 120 b 1, the wiring layer13 b, the wiring layer 15 b, and the contact metal layer 20. Theelectrically-conductive plugs 120 a 2 and 120 b 2 are desirablyconfigured by, for example, a stacked film of a metal material such astitanium (Ti), titanium nitride (TiN), and tungsten, in order to allowthe electrically-conductive plugs 120 a 2 and 120 b 2 to function alsoas a light-shielding film. Further, the use of such a stacked film isdesirable because this enables a contact with silicon to be secured alsoin a case where the electrically-conductive plugs 120 a 1 and 120 b 1are each formed as an n-type or p-type semiconductor layer.

The interlayer insulating film 12 is desirably configured by aninsulating film having a small interface state in order to reduce theinterface state with the semiconductor substrate 11 (silicon layer 110)and to suppress occurrence of a dark current from an interface with thesilicon layer 110. As such an insulating film, for example, a stackedfilm of a hafnium oxide (HfO₂) film and a silicon oxide (SiO₂) film maybe used. The interlayer insulating film 14 is configured by a monolayerfilm made of one of silicon oxide, silicon nitride, and siliconoxynitride (SiON), for example, or alternatively is configured by astacked film made of two or more thereof.

The insulating film 16 is configured by a monolayer film made of one ofsilicon oxide, silicon nitride, and silicon oxynitride (SiON), forexample, or alternatively is configured by a stacked film made of two ormore thereof. The insulating film 16 has a surface that is, for example,planarized, and has a substantially stepless shape and pattern withrespect to the lower electrode 15 a. The insulating film 16 has afunction of electrically separating the electrodes 15 a of therespective pixels from one another in a case where the photoelectricconversion element 10 is used as a pixel of the solid-state imagingdevice.

The lower electrode 15 a is provided at a region that faceslight-receiving surfaces of the inorganic photoelectric conversionsections 11B and 11R formed inside the semiconductor substrate 11 andcovers the light-receiving surfaces. The lower electrode 15 a isconfigured by an electrically-conductive film havinglight-transmissivity, and is made of an indium tin oxide (ITO), forexample. However, as a constituent material of the lower electrode 15 a,a dopant-doped tin oxide (SnO₂)-based material or a zinc oxide-basedmaterial in which aluminum zinc oxide (ZnO) is doped with a dopant maybe used, besides the ITO. Examples of the zinc oxide-based materialinclude aluminum zinc oxide (AZO) doped with aluminum (Al) as a dopant,gallium (Ga)-doped gallium zinc oxide (GZO), and indium (In)-dopedindium zinc oxide (IZO). Aside from those mentioned above, for example,CuI, InSbO₄, ZnMgO, CulnO₂, MgIN₂O₄, CdO, and ZnSnO₃ may be used. It isto be noted that, in the present embodiment, a signal electric charge(electron) is extracted from the lower electrode 15 a; thus, in thesolid-state imaging device described later using the photoelectricconversion element 10 as a pixel, the lower electrode 15 a is formed ina manner separated on a pixel-by-pixel basis.

The organic photoelectric conversion layer 17 includes a fullerenehaving undergone polysubstituted modification (fullerene derivative),together with an organic semiconductor that performs photoelectricconversion of light of a selective wavelength region while transmittinglight of any other wavelength region.

The organic semiconductor desirably includes one or both of an organicp-type semiconductor and an organic n-type semiconductor. As such anorganic semiconductor, one of a quinacridone derivative, a naphthalenederivative, an anthracene derivative, a phenanthrene derivative, atetracene derivative, a pyrene derivative, a perylene derivative, and afluoranthene derivative may be preferably used. Alternatively, a polymersuch as phenylenevinylene, fluorene, carbazole, indole, pyrene, pyrrole,picoline, thiophene, acetylene, and diacetylene, or a derivative thereofmay be used. In addition, a condensed polycyclic aromatic compound and achain compound in which an aromatic cyclic or heterocyclic compound iscondensed, such as a metal complex dye, a cyanine dye, merocyanine dye,a phenylxanthene dye, a triphenylmethane dye, a rhodacyanine dye, axanthene dye, a macrocyclic azaannulene dye, an azulene dye,naphthoquinone, an anthraquinone dye, anthracene, and pyrene may bepreferably used. Alternatively, two nitrogen-containing heterocyclicrings such as quinolines, benzothiazoles, and benzoxazoles each having asquarylium group and a croconic methine group as a linking chain, or acyanine-like dye, etc., linked by the squarylium group and the croconicmethine group may be preferably used. It is to be noted that, as theabove-mentioned metal complex dye, a dithiol metal complex dye, a metalphthalocyanine dye, a metal porphyrin dye, or a ruthenium complex dye ispreferred; however, this is not limitative. In the present embodiment,the organic photoelectric conversion layer 17 is able to performphotoelectric conversion of green light that corresponds to a portion orall of a wavelength region of 495 nm to 570 nm, for example. Such anorganic photoelectric conversion layer 17 has a thickness of 50 nm to500 nm, for example.

As the fullerene derivative, so-called C₆₀ fullerene, as a motherskeleton, having 60 carbon atoms preferably undergoes multiplemodification by any of substituents. Specifically, the C₆₀ fullerene isdesirably modified by a substituent having an absorbance smaller thanthat of the fullerene in a visible range. This shifts an absorptionwavelength peak of the fullerene toward shorter wavelength side, thusreducing an influence on a spectroscopic shape of light absorbed by theorganic semiconductor. It is to be noted that the visible range as usedhere refers to a range from 380 nm to 700 nm.

As the substituent having an absorbance smaller than that of thefullerene in the visible range, for example, a hydrogen atom, halogen(F, Cl, Br, and I) atoms, a hydroxyl group, an alkyl group, and a groupcontaining a chalcogen element, as well as substituents made ofcompounds listed in Tables 1 to 3 may be used. It is to be noted thatFIG. 1 also sets forth, as references, absorption wavelengths andabsorbance indexes in situations where the fullerene is dissolved inhexane. Further, it is appreciated that, in a small substituent made ofa single atom such as the above-described hydrogen atom and halogen atomor made of a plurality of atoms, the substituent itself has a smallabsorbance when taking benzene as a reference.

TABLE 1 λ_(max)/ log ε/ Compound Solvent nm mol⁻¹ · dm³ · cm⁻¹ FullereneHexane 213 5.13 257 5.24 329 4.71 440-670 2.80 Benzene Iso-Octane 2622.09 255 2.25 247.5 2.15 243.5 1.96 237.5 1.73 234 1.51 ChlorobenzeneOctane 272 2.26 264.5 2.37 261.5 2.24 258 2.27 251.5 2.08 245 1.86 233.51.37 Fluorobenzene Iso-Octane 266 2.95 260 3.02 254.5 2.83 249 2.31 2043.90 Toluene Water 260 2.48 206 3.78 Phenol Cyclohexane 276 3.32 2693.34 263 3.78 210 3.84

TABLE 2 λ_(max)/ log ε/ Compound Solvent nm mol⁻¹ · dm³ · cm⁻¹Acetophenone Hexane 325 1.70 286.5 2.90 277 3.00 237 4.11 AcetanilideCyclohexane 282 2.82 274 2.93 238 4.13 Benzoic Acid Cyclohexane 282 2.96274 3.02 268 2.91 232 4.10 Benzonitrile Iso-Octane 291.5 1.07 278 1.16276.5 2.81 268 2.80 264 2.65 262.5 2.64 258 2.47 252 2.25 229.5 4.05 2254.07 221 4.09 Nitrobenzene Gas 340 2.15 288 2.70 240 3.93 193 4.24 1644.44

TABLE 3 λ_(max)/ log ε/ Compound Solvent nm mol⁻¹ · dm³ · cm⁻¹ AnilineIso-Octane 295 3.10 291 3.22 287.5 3.28 284 3.24 280 3.20 277 3.12 2712.96 234.5 3.94 Pyrrole Hexane 240 2.48 210 4.18 Furan Hexane 200 4.00Thiophene Iso-Octane 231.5 3.73 Carbazole Chloroform 333 3.51 309 3.80298 3.60 292 4.23 Dibenzothiophene Ethanol 324 3.41 286 4.02 235 4.61Thiazole Ethanol 240 3.60 Copper Pyridine 676 5.17 Phthalocyanine 6094.37 345 4.59

Examples of the specific fullerene derivative include a compoundrepresented by the following formula (1):

where R denotes, each independently, a hydrogen atom, a halogen atom, alinear, branched or cyclic alkyl group, a phenyl group, a group having alinear or condensed aromatic compound, a group having a halide, apartial fluoroalkyl group, a perfluoroalkyl group, a silyl alkyl group,a silyl alkoxy group, an aryl silyl group, an arylsulfanyl group, analkylsulfanyl group, an arylsulfonyl group, an alkylsulfonyl group, anaryl sulfide group, an alkyl sulfide group, an amino group, analkylamino group, an arylamino group, a hydroxy group, an alkoxy group,an acylamino group, an acyloxy group, a carbonyl group, a carboxy group,a carboxoamido group, a carboalkoxy group, an acyl group, a sulfonylgroup, a cyano group, a nitro group, a group having a chalcogenide, aphosphine group, a phosphonic group, or a derivative thereof, providedthat n is an integer of 2 or more.

It is to be noted that a substituent that modifies the fullerene is notlimited to the above-mentioned substituent; any substituent not havingabsorption in the visible range suffices.

The number of the substituent that modifies the fullerene may be two ormore as described above, and may be particularly preferably 16 or more;the upper limit of the number is 48 or less, for example. This makes itpossible to shift the absorption wavelength peak of the fullerenederivative toward shorter wavelength side.

It is to be noted that the fullerene derivative may be varied to have adesired work function depending on types of the substituent. Forexample, in a case of using the fullerene derivative as the n-typesemiconductor, it is preferable to use, as the substituent, for example,a halogen atom such as fluoride having a high electron-withdrawingproperty. In a case of using the fullerene derivative as the p-typesemiconductor, it is preferable to use a carbon atom or a hydrogen atomhaving a high electron-donating property.

Further, the fullerene derivative is not limited to the C₆₀ fullerene,and may have, as the mother skeleton, a so-called high-order fullerenehaving more than 60 carbon atoms.

Any other unillustrated layer may be provided between the organicphotoelectric conversion layer 17 and the lower electrode 15 a andbetween the organic photoelectric conversion layer 17 and the upperelectrode 18. For example, an underlying film, a hole transport layer,an electron blocking film, the organic photoelectric conversion layer17, a hole blocking film, a buffer film, an electron transport layer,and a work function adjustment film may be stacked in order from side ofthe lower electrode 15 a. The above-described fullerene derivative maybe used as the electron blocking film, the hole blocking film, theelectron transport layer, and the hole transport layer.

The upper electrode 18 is configured by the electrically-conductive filmhaving light-transmissivity similarly to that of the lower electrode 15a. In the solid-state imaging device using the photoelectric conversionelement 10 as a pixel, the upper electrode 18 may be separated on apixel-by-pixel basis, or may be formed as a common electrode for therespective pixels. The upper electrode 18 has a thickness of 10 nm to200 nm, for example.

The protective film 19 is made of a material havinglight-transmissivity, and is, for example, a monolayer film made of oneof silicon oxide, silicon nitride, and silicon oxynitride, oralternatively is a stacked film made of two or more thereof. Theprotective film 19 has a thickness of 100 nm to 30,000 nm, for example.

The contact metal layer 20 is made of one of titanium, tungsten,titanium nitride, and aluminum, for example, or alternatively isconfigured by a stacked film made of two or more thereof.

The upper electrode 18 and the protective film 19 are provided to coverthe organic photoelectric conversion layer 17, for example. FIG. 2illustrates a planar configuration of the organic photoelectricconversion layer 17, the protective film 19 (upper electrode 18), andthe contact hole H.

Specifically, a peripheral part e2 of the protective film 19 (applicablelikewise to the upper electrode 18) is located outside a peripheral parte1 of the organic photoelectric conversion layer 17. The protective film19 and the upper electrode 18 are formed to be expanded outward beyondthe organic photoelectric conversion layer 17. In detail, the upperelectrode 18 is formed to cover a top surface and side surfaces of theorganic photoelectric conversion layer 17 and to extend up to a part onthe insulating film 16. The protective film 19 is formed to cover a topsurface of such an upper electrode 18 and to have a planar shape similarto that of the upper electrode 18. The contact hole H is provided in aregion (region outside the peripheral part e1), of the protective film19, that does not face the organic photoelectric conversion layer 17.Thus, a portion of a front surface of the upper electrode 18 is exposed.A distance from the peripheral part e1 to the peripheral part e2 is, forexample, 1 μm to 500 μm, although the distance is not particularlylimited. It is to be noted that although FIG. 2 illustrates a singlerectangular contact hole H provided along an edge side of the organicphotoelectric conversion layer 17, the shape and the number of thecontact hole H are not limited thereto; other shapes (e.g., circularshape and square shape) may be adopted, and a plurality of contact holesH may be provided.

A planarization film 21 is formed on the protective film 19 and thecontact metal layer 20 to cover the whole surface. An on-chip lens 22(microlens) is provided on the planarization film 21. The on-chip lens22 condenses light incident from above to each light-receiving surfaceof the organic photoelectric conversion section 11G, and the inorganicphotoelectric conversion sections 11B and 11R. In the presentembodiment, the multi-layer wiring layer 51 is formed on side of thesurface S2 of the semiconductor substrate 11, thus making it possible toallow the respective light-receiving surfaces of the organicphotoelectric conversion section 11G and the inorganic photoelectricconversion sections 11B and 11R to be disposed closer to one another.Thus, it becomes possible to reduce a variation in sensitivity amongrespective colors occurring depending on F value of the on-chip lens 22.

It is to be noted that, in the photoelectric conversion element 10according to the present embodiment, a signal electric charge (electron)is extracted from the lower electrode 15 a, and thus the solid-stateimaging device using the photoelectric conversion element 10 as a pixelmay adopt the upper electrode 18 as a common electrode. In this case,the above-described transmission path configured by the contact hole H,the contact metal layer 20, the wiring layers 15 b and 13 b, and theelectrically-conductive plugs 120 b 1 and 120 b 2 may be formed at atleast one location for all of the pixels.

In the semiconductor substrate 11, for example, the inorganicphotoelectric conversion sections 11B and 11R and the green electricitystorage layer 110G are formed to be embedded in a predetermined regionof the n-type silicon (Si) layer 110. Further, theelectrically-conductive plugs 120 a 1 and 120 b 1 are embedded in thesemiconductor substrate 11. The electrically-conductive plugs 120 a 1and 120 b 1 serve as a transmission path of an electric charge (electronor hole (hole)) from the organic photoelectric conversion section 11G.In the present embodiment, the rear surface (surface 51) of thesemiconductor substrate 11 serves as a light-receiving surface. On sideof the front surface (surface S2) of the semiconductor substrate 11, aplurality of pixel transistors (including transfer transistors Tr1 toTr3) corresponding, respectively, to the organic photoelectricconversion section 11G and the inorganic photoelectric conversionsections 11B and 11R, are formed, and a peripheral circuit configured bya logic circuit, etc., is formed.

Examples of the pixel transistors include a transfer transistor, a resettransistor, an amplifying transistor, and a selection transistor. Eachof the transistors is configured, for example, by a MOS transistor, andis formed in a p-type semiconductor well region on side of the surfaceS2. A circuit that includes such pixel transistors is formed for each ofthe photoelectric conversion sections for red, green, and blue colors.Each of the circuits may have a three-transistor configuration thatincludes three transistors in total, configured by the transfertransistor, the reset transistor, and the amplifying transistor, forexample, among these pixel transistors. Alternatively, each of thecircuits may have a four-transistor configuration that includes theselection transistor in addition thereto. Here, illustration anddescription are given only of the transfer transistors Tr1 to Tr3 amongthese pixel transistors. Further, the pixel transistor other than thetransfer transistors may be shared by the photoelectric conversionsections or by the pixels. Furthermore, a so-called pixel-sharedstructure may also be applied in which a floating diffusion is shared.

The transfer transistors Tr1 to Tr3 each include a gate electrode (gateelectrode TG1, TG2, or TG3) and a floating diffusion (FD113, FD114, orFD116). The transfer transistor Tr1 transfers, to a vertical signal lineLsig described later, a signal electric charge (electron, in the presentembodiment) corresponding to a green color that is generated in theorganic photoelectric conversion section 11G and is accumulated in thegreen electricity storage layer 110G. The transfer transistor Tr2transfers, to the vertical signal line Lsig described later, a signalelectric charge (electron, in the present embodiment) corresponding to ablue color that is generated and accumulated in the inorganicphotoelectric conversion section 11B. Likewise, the transfer transistorTr3 transfers, to the vertical signal line Lsig described later, asignal electric charge (electron, in the present embodiment)corresponding to a red color that is generated and accumulated in theinorganic photoelectric conversion section 11R.

The inorganic photoelectric conversion sections 11B and 11R are each aphotodiode (Photo Diode) that has a pn junction. The inorganicphotoelectric conversion sections 11B and 11R are formed in order fromside of the surface S1 on an optical path in the semiconductor substrate11. Among these, the inorganic photoelectric conversion section 11Bselectively detects blue light and accumulates a signal electric chargecorresponding to the blue color. The inorganic photoelectric conversionsection 11B is formed to extend, for example, from a selective regionalong the surface S1 of the semiconductor substrate 11 to a region nearan interface with the multi-layer wiring layer 51. The inorganicphotoelectric conversion section 11R selectively detects red light andaccumulates a signal electric charge corresponding to the red color. Theinorganic photoelectric conversion section 11R is formed, for example,in a region in a lower layer (on surface S2 side) than the inorganicphotoelectric conversion section 11B. It is to be noted that the blue(B) is a color that corresponds to a wavelength region from 450 nm to495 nm, for example, and the red (R) may be a color that corresponds toa wavelength region from 620 nm to 750 nm, for example. It is enoughthat the inorganic photoelectric conversion sections 11B and 11R areable to detect light of a portion or all of the respective wavelengthregions described above.

FIG. 3A illustrates a detailed configuration example of the inorganicphotoelectric conversion sections 11B and 11R. FIG. 3B corresponds to aconfiguration in another cross-section in FIG. 3A. It is to be notedthat, in the present embodiment, description is given of a case where,among a pair of an electron and a hole generated by photoelectricconversion, the electron is read as a signal electric charge (case wherean n-type semiconductor region serves as a photoelectric conversionlayer). Further, in the diagram, “+(plus)” attached above “p” or “n”indicates that p-type or n-type impurity concentration is high.Furthermore, among the pixel transistors, the gate electrodes TG2 andTG3 of the transfer transistors Tr2 and Tr3 are also illustrated.

The inorganic photoelectric conversion section 11B includes, forexample, a p-type semiconductor region (hereinafter, simply referred toas “p-type region”, applicable likewise to the case of n-type) 111 p toserve as a hole accumulation layer, and an n-type photoelectricconversion layer (n-type region) 111 n to serve as an electronaccumulation layer. The p-type region 111 p and the n-type photoelectricconversion layer 111 n are each formed in a selective region near thesurface S1. A portion of each of the p-type region 111 p and the n-typephotoelectric conversion layer 111 n is bent and formed to extend toreach the interface with the surface S2. The p-type region 111 p iscoupled to an unillustrated p-type semiconductor well region on side ofthe surface S1. The n-type photoelectric conversion layer 111 n iscoupled to the FD113 (n-type region) of the transfer transistor Tr2 forthe blue color. It is to be noted that a p-type region 113 p (holeaccumulation layer) is formed near an interface between the surface S2and each of the end portions of the p-type region 111 p and the n-typephotoelectric conversion layer 111 n on side of the surface S2.

The inorganic photoelectric conversion section 11R is formed, forexample, by p-type regions 112 p 1 and 112 p 2 (hole accumulationlayers), with an n-type photoelectric conversion layer 112 n (electronaccumulation layer) being interposed therebetween (has a p-n-p stackedstructure). A portion of the n-type photoelectric conversion layer 112 nis bent and formed to extend to reach the interface with the surface S2.The n-type photoelectric conversion layer 112 n is coupled to the FD 114(n-type region) of the transfer transistor Tr3 for the red color. It isto be noted that the p-type region 113 p (hole accumulation layer) isformed at least near the interface between the surface S2 and an endportion of the n-type photoelectric conversion layer 111 n on side ofthe surface S2.

FIG. 4 illustrates a detailed configuration example of the greenelectricity storage layer 110G. It is to be noted that description isgiven here of a case where, among a pair of an electron and a holegenerated by the organic photoelectric conversion section 11G, theelectron is read as a signal electric charge from side of the lowerelectrode 15 a. Further, FIG. 4 also illustrates the gate electrode TG1of the transfer transistor Tr1 among the pixel transistors.

The green electricity storage layer 110G includes an n-type region 115 nthat serves as an electron accumulation layer. A portion of the n-typeregion 115 n is coupled to the electrically-conductive plug 120 a 1, andaccumulates electrons supplied from side of the lower electrode 15 a viathe electrically-conductive plug 120 a 1. The n-type region 115 n isalso coupled to the FD 116 (n-type region) of the transfer transistorTr1 for the green color. It is to be noted that a p-type region 115 p(hole accumulation layer) is formed near an interface between the n-typeregion 115 n and the surface S2.

The electrically-conductive plugs 120 a 1 and 120 b 1, together with theelectrically-conductive plugs 120 a 2 and 120 b 2 described later, eachfunction as a connector between the organic photoelectric conversionsection 11G and the semiconductor substrate 11, and forms a transmissionpath for electrons or holes generated in the organic photoelectricconversion section 11G. In the present embodiment, theelectrically-conductive plug 120 a 1 is conducted to the lower electrode15 a of the organic photoelectric conversion section 11G, and is coupledto the green electricity storage layer 110G. The electrically-conductiveplug 120 b 1 is conducted to the upper electrode 18 of the organicphotoelectric conversion section 11G, and serves as a wiring line fordischarge of holes.

These electrically-conductive plugs 120 a 1 and 120 b 1 are eachconfigured, for example, by an electrically-conductive typesemiconductor layer, and are each formed to be embedded in thesemiconductor substrate 11. In this case, the electrically-conductiveplug 120 a 1 may be favorably of an n-type (because it serves as thetransmission path of electrons). The electrically-conductive plug 120 b1 may be favorably of a p-type (because it serves as the transmissionpath of holes). Alternatively, the electrically-conductive plugs 120 a 1and 120 b 1 may be each made of, for example, an electrically-conductivefilm material such as tungsten embedded in a through-via. In this case,for example, in order to suppress short circuit with silicon, a sidesurface of the via is desirably covered with an insulating film made ofa material such as silicon oxide (SiO₂) and silicon nitride (SiN).

The multi-layer wiring layer 51 is formed on the surface S2 of thesemiconductor substrate 11. In the multi-layer wiring layer 51, aplurality of wiring lines 51 a are arranged with an interlayerinsulating film 52 being interposed therebetween. In this manner, themulti-layer wiring layer 51 is formed on side opposite to thelight-receiving surface in the photoelectric conversion element 10.Thus, a so-called backside illumination type solid-state imaging deviceis achievable. A support substrate 53 made of silicon, for example, isjoined to the multi-layer wiring layer 51.

(1-2. Manufacturing Method)

For example, it is possible to manufacture the photoelectric conversionelement 10 as follows. FIGS. 5A, 5B, 6A, 6B, 7A, 7B, and 7C illustrate amanufacturing method of the photoelectric conversion element 10 in orderof steps. It is to be noted that FIGS. 7A, 7B, and 7C illustrate only aconfiguration of a main part of the photoelectric conversion element 10.

First, the semiconductor substrate 11 is formed. Specifically, aso-called SOI substrate is prepared, in which the silicon layer 110 isformed on a silicon base 1101 with a silicon oxide film 1102 beinginterposed therebetween. It is to be noted that a surface on side of thesilicon oxide film 1102 of the silicon layer 110 serves as a rearsurface (surface S1) of the semiconductor substrate 11. FIGS. 5A and 5Billustrate the structure illustrated in FIG. 1 in a vertically invertedstate. Subsequently, as illustrated in FIG. 5A, theelectrically-conductive plugs 120 a 1 and 120 b 1 are formed in thesilicon layer 110. In this situation, it is possible to form theelectrically-conductive plugs 120 a 1 and 120 b 1, for example, byforming through-vias in the silicon layer 110 and thereafter embedding,inside the through-vias, tungsten and barrier metal such as theabove-described silicon nitride. Alternatively, for example, ionimplantation into the silicon layer 110 may be adopted to form anelectrically conductive impurity semiconductor layer. In this case, theelectrically-conductive plugs 120 a 1 and 120 b 1 are formed,respectively, as an n-type semiconductor layer and a p-typesemiconductor layer. Thereafter, for example, the inorganicphotoelectric conversion sections 11B and 11R each having the p-typeregion and n-type region illustrated in FIG. 3A are formed by ionimplantation in regions having different depths inside the silicon layer110 (so as to overlap each other). Further, the green electricitystorage layer 110G is formed by ion implantation at a region adjacent tothe electrically-conductive plug 120 a 1. In this manner, thesemiconductor substrate 11 is formed.

Subsequently, the pixel transistor including the transfer transistorsTr1 to Tr3, and the peripheral circuit such as a logic circuit areformed on side of the surface S2 of the semiconductor substrate 11.Thereafter, as illustrated in FIG. 5B, the plurality of wiring lines 51a are formed on the surface S2 of the semiconductor substrate 11, withthe interlayer insulating film 52 being interposed therebetween tothereby form the multi-layer wiring layer 51. Subsequently, the supportsubstrate 53 made of silicon is joined onto the multi-layer wiring layer51. Thereafter, the silicon base 1101 and the silicon oxide film 1102are peeled off from side of the surface 51 of the semiconductorsubstrate 11 to expose the surface 51 of the semiconductor substrate 11.

Next, the organic photoelectric conversion section 11G is formed on thesurface 51 of the semiconductor substrate 11. Specifically, asillustrated in FIG. 6A, first, the interlayer insulating film 12configured by the stacked film of a hafnium oxide film and a siliconoxide film as described above is formed on the surface 51 of thesemiconductor substrate 11. For example, the hafnium oxide film isformed by an atomic layer deposition (ALD) method, and thereafter, forexample, the silicon oxide film is formed by a plasma chemical vapordeposition (CVD) method. Thereafter, contact holes H1 a and H1 b areformed at locations corresponding to the respectiveelectrically-conductive plugs 120 a 1 and 120 b 1 of the interlayerinsulating film 12. The electrically-conductive plugs 120 a 2 and 120 b2 made of the above-described material are formed to fill the contactholes H1 a and H1 b, respectively. In this situation, theelectrically-conductive plugs 120 a 2 and 120 b 2 may be each formed toexpand to a region that is desired to be light-shielded (to cover theregion that is desired to be light-shielded). Alternatively, alight-shielding layer may be formed at a region separated from theelectrically-conductive plugs 120 a 2 and 120 b 2.

Subsequently, as illustrated in FIG. 6B, the interlayer insulating film14 made of the above-described material is formed by the plasma CVDmethod, for example. It is to be noted that, after the formation of thefilm, a surface of the interlayer insulating film 14 is desirablyplanarized by a chemical mechanical polishing (CMP) method, for example.Next, contact holes are opened at locations corresponding to theelectrically-conductive plugs 120 a 2 and 120 b 2 of the interlayerinsulating film 14. The contact holes are filled with theabove-described material to form the wiring layers 13 a and 13 b. It isto be noted that the CMP method, for example, may be desirably usedthereafter to remove a residual wiring layer material (such as tungsten)on the interlayer insulating film 14. Next, the lower electrode 15 a isformed on the interlayer insulating film 14. Specifically, first, theabove-described transparent electrically-conductive film is formedthroughout the entire surface of the interlayer insulating film 14 by asputtering method, for example. Thereafter, a photolithography method isused (exposure, development, post-bake, etc. of a photoresist film isperformed), and a selective part is removed by dry etching or wetetching, for example, thus forming the lower electrode 15 a. In thissituation, the lower electrode 15 a is formed at a region that faces thewiring layer 13 a. Further, upon the process of the transparentelectrically-conductive film, the transparent electrically-conductivefilm is allowed to remain also at a region that faces the wiring layer13 b, thereby forming the wiring layer 15 b that constitutes a portionof the transmission path of holes, together with the lower electrode 15a.

Subsequently, the insulating film 16 is formed. In this situation,first, the insulating film 16 made of the above-described material isformed, for example, by the plasma CVD method throughout the entiresurface of the semiconductor substrate 11 to cover the interlayerinsulating film 14, the lower electrode 15 a, and the wiring layer 15 b.Thereafter, as illustrated in FIG. 7A, the formed insulating film 16 ispolished, for example, by the CMP method. Thus, the lower electrode 15 aand the wiring layer 15 b are exposed from the insulating film 16, and astep difference between the lower electrode 15 a and the insulating film16 are moderated (desirably planarized).

Next, as illustrated in FIG. 7B, the organic photoelectric conversionlayer 17 is formed on the lower electrode 15 a. In this situation, aphotoelectric conversion material made of the above-described materialis patterned to be formed by a vacuum deposition method using a metalmask, for example. It is to be noted that, as described above, whenother organic layers (such as electron blocking layer) are formed as anupper layer or a lower layer of the organic photoelectric conversionlayer 17, it is desirable to form the layers successively in a vacuumprocess (through a vacuum consistent process) using the same metal mask.Further, the film-forming method of the organic photoelectric conversionlayer 17 is not necessarily limited to the above-described method usingthe metal mask; any other method, for example, a printing technique maybe used.

Subsequently, as illustrated in FIG. 7C, the upper electrode 18 and theprotective film 19 are formed. First, the upper electrode 18 configuredby the above-described transparent electrically-conductive film isformed, by the vacuum deposition method or the sputtering method, forexample, throughout the entire surface of the substrate to cover the topsurface and the side surfaces of the organic photoelectric conversionlayer 17. It is to be noted that the upper electrode 18 is desirablyformed with the organic photoelectric conversion layer 17 through thevacuum consistent process, because characteristics of the organicphotoelectric conversion layer 17 are easily varied under influences ofmoisture, oxygen, hydrogen, etc. Thereafter (before patterning of theupper electrode 18), the protective film 19 made of the above-describedmaterial is formed by the plasma CVD method, for example, to cover thetop surface of the upper electrode 18. Subsequently, the protective film19 is formed on the upper electrode 18, and thereafter the upperelectrode 18 is processed.

Thereafter, etching by means of the photolithography method is used tocollectively remove a selective part of each of the upper electrode 18and the protective film 19. Subsequently, the contact hole H is formedin the protective film 19, for example, by the etching by means of thephotolithography method. In this situation, the contact hole H isdesirably formed in a region not facing the organic photoelectricconversion layer 17. Even after the formation of the contact hole H, asdescribed above, the photoresist is peeled off, and washing usingchemical solution is performed in a manner similar to that describedabove. Thus, it follows that the upper electrode 18 is exposed from theprotective film 19 at the region facing the contact hole H. Therefore,in consideration of generation of a pin hole as described above, theregion where the organic photoelectric conversion layer 17 is formed isdesirably avoided to provide the contact hole H. Subsequently, thecontact metal layer 20 made of the above-described material is formedusing the sputtering method, for example. In this situation, the contactmetal layer 20 is formed on the protective film 19 to fill the contacthole H and to extend up to the top surface of the wiring layer 15 b.Finally, the planarization film 21 is formed throughout the entiresurface of the semiconductor substrate 11, and thereafter the on-chiplens 22 is formed on the planarization film 21 to complete thephotoelectric conversion element 10 illustrated in FIG. 1.

As a pixel of the solid-state imaging device, the photoelectricconversion element 10 as described above, for example, obtains a signalelectric charge as follows. That is, as illustrated in FIG. 8, whenlight L is incident through the on-chip lens 22 (not illustrated in FIG.8), the light L passes through the organic photoelectric conversionsection 11G and the inorganic photoelectric conversion sections 11B and11R in order, and undergoes photoelectric conversion of each color ofred, green, and blue through the passing process. FIG. 9 schematicallyillustrates a flow in which the signal electric charge (electron) isobtained on the basis of the incident light. Description is given belowof a specific operation of signal obtainment in each of thephotoelectric conversion sections.

(Obtainment of Green Signal by Organic Photoelectric Conversion Section11G)

Green light Lg, among the light L incident on the photoelectricconversion element 10, is first detected (absorbed) selectively in theorganic photoelectric conversion section 11G to undergo thephotoelectric conversion. Accordingly, an electron Eg of theelectron-hole pair generated is extracted from side of the lowerelectrode 15 a, and thereafter is accumulated in the green electricitystorage layer 110G through a transmission path A (wiring layer 13 a andelectrically-conductive plugs 120 a 1 and 120 a 2). The accumulatedelectron Eg is transferred to the FD 116 upon a reading operation. It isto be noted that a hole Hg is discharged from side of the upperelectrode 18 through a transmission path B (contact metal layer 20,wiring layers 13 b and 15 b, and electrically-conductive plugs 120 b 1and 120 b 2).

Specifically, the signal electric charge is accumulated as follows. Thatis, in the present embodiment, for example, a predetermined negativepotential VL (<0 V) is applied to the lower electrode 15 a, and apotential VU (<VL) lower than the potential VL is applied to the upperelectrode 18. It is to be noted that the potential VL is supplied, forexample, from the wiring line 51 a inside the multi-layer wiring layer51 to the lower electrode 15 a through the transmission path A. Thepotential VL is supplied, for example, from the wiring line 51 a insidethe multi-layer wiring layer 51 to the upper electrode 18 through thetransmission path B. Accordingly, in a state where an electric charge isaccumulated (where the unillustrated reset transistor and the transfertransistor Tr1 are each in an OFF state), the electron, among theelectron-hole pair generated in the organic photoelectric conversionlayer 17, is guided toward side of the lower electrode 15 a having arelatively high potential (the hole is guided toward side of the upperelectrode 18). In this manner, the electron Eg is extracted from thelower electrode 15 a, and is accumulated in the green electricitystorage layer 110G (n-type region 115 n, in detail) through thetransmission path A. Further, the accumulation of the electron Eg alsocauses the potential VL of the lower electrode 15 a conducted to thegreen electricity storage layer 110G to fluctuate. This amount of thevariation in the potential VL corresponds to the signal potential (here,potential of a green signal).

Further, upon the reading operation, the transfer transistor Tr1 isturned into an ON state, and the electron Eg accumulated in the greenelectricity storage layer 110G is transferred to the FD116. This causesthe green signal based on a light reception amount of the green light Lgto be read by the vertical signal line Lsig described later throughunillustrated another pixel transistor. Thereafter, the unillustratedreset transistor and the transfer transistor Tr1 are turned into an ONstate, and the FD116 being the n-type region and an electricity storageregion of the green electricity storage layer 110G (n-type region 115 n)are reset to a power supply voltage VDD, for example.

(Obtainment of Blue Signal and Red Signal by Inorganic PhotoelectricConversion Sections 11B and R)

Subsequently, among the light having been transmitted through theorganic photoelectric conversion section 11G, blue light and red lightare absorbed in order, respectively, in the inorganic photoelectricconversion section 11B and the inorganic photoelectric conversionsection 11R to each undergo the photoelectric conversion. In theinorganic photoelectric conversion section 11B, an electron Ebcorresponding to incident blue light is accumulated in the n-type region(n-type photoelectric conversion layer 111 n), and the accumulatedelectron Ed is transferred to the FD 113 upon the reading operation. Itis to be noted that the hole is accumulated in the unillustrated p-typeregion. Likewise, in the inorganic photoelectric conversion section 11R,an electron Er corresponding to the incident red light is accumulated inthe n-type region (n-type photoelectric conversion layer 112 n), and theaccumulated electron Er is transferred to the FD 114 upon the readingoperation. It is to be noted that the hole is accumulated in theunillustrated p-type region.

As described above, in the state where the electric charge isaccumulated, the negative potential VL is applied to the lower electrode15 a of the organic photoelectric conversion section 11G. Thus, thep-type region (p-type region 111 p in FIG. 2) being the holeaccumulation layer of the inorganic photoelectric conversion section 11Btends to have an increased hole concentration. Accordingly, it becomespossible to suppress occurrence of a dark current at the interfacebetween the p-type region 111 p and the interlayer insulating film 12.

Upon the reading operation, similarly to the above-described organicphotoelectric conversion section 11G, the transfer transistors Tr2 andTr3 are turned into an ON state, and the electrons Eb and Eraccumulated, respectively, in the n-type photoelectric conversion layers111 n and 112 n are transferred, respectively, to the FD113 and FD114.This causes each of the blue signal based on a light reception amount ofthe blue light Lb and the red signal based on a light reception amountof the red light Lr to be read by the vertical signal line Lsigdescribed later through unillustrated another pixel transistor.Thereafter, the unillustrated reset transistor and the transfertransistors Tr2 and Tr3 are turned into an ON state, and the FD113 andFD114 being the n-type region are reset to the power supply voltage VDD,for example.

In this manner, by stacking the organic photoelectric conversion section11G and the inorganic photoelectric conversion sections 11B and 11R inthe vertical direction, it becomes possible to detect pieces of colorlight of red, green, and blue separately without providing a colorfilter, thus allowing a signal electric charge of each color to beobtained. This makes it possible to suppress optical loss (reduction insensitivity) caused by color light absorption by the color filter aswell as occurrence of a false color associated with a pixelinterpolation process.

(1-3. Workings and Effects)

As described above, in recent years, a solid-state imaging device suchas the CCD image sensor and the CMOS image sensor has been requested tohave high sensitivity, low noise, and high color reproducibility. Inorder to achieve these, a solid-state imaging device has been developed.The solid-state imaging device includes an organic photoelectricconversion section that detects green light and generates a signalelectric charge in accordance with the green light and photodiodes(inorganic photoelectric conversion sections) that detect red light andblue light, respectively, to obtain three color signals in a singlepixel, thus allowing for improvement in a photoelectric conversionefficiency in the single pixel as well as improvement in thesensitivity. Further, a photoelectric conversion element, etc., has beendeveloped. The photoelectric conversion element, etc., has furtherenhanced optical conversion efficiency by adding, together with aphotoelectric conversion dye, the fullerene or the fullerene derivativeto the photoelectric conversion film.

However, the solid-state imaging device, using the photoelectricconversion element, to which the fullerene or the derivative thereof issimply added has issues as follows. A broad absorption spectrum appearsdue to an interaction between fullerenes, and the spectroscopic shape oflight selectively absorbed by the photoelectric conversion dye isdeteriorated, thus lowering the color reproducibility.

Thus, in the present embodiment, the organic semiconductor as thephotoelectric conversion dye and the fullerene having undergonepolysubstituted modification (fullerene derivative) are used for theorganic photoelectric conversion layer 17 provided between the lowerelectrode 15 a and the upper electrode 18.

FIG. 10 illustrates ultraviolet visible absorption spectra (UV-vis),standardized with a film thickness, of C₆₀F₃₆ that is one ofpolysubstituted fullerenes and of a fullerene (C₆₀) as a comparativeexample. The ultraviolet visible absorption spectra of C₆₀F₃₆ and C₆₀were each measured by producing a thin film having a thickness of 50 nmon quartz using a vacuum deposition equipment. It can be appreciatedfrom FIG. 10 that C₆₀ has a broad absorption in a visible range equal toor lower than 600 nm, whereas C₆₀F₃₆ does not have a maximum absorptionnear the visible range (ranging from 380 nm to 700 nm). Therefore, itcan be seen that C₆₀F₃₆ has a lower absorbance than that of C₆₀.

FIG. 11 illustrates ultraviolet visible absorption spectra (UV-vis) ofvarious fullerene derivatives. The ultraviolet visible absorptionspectra of the various fullerene derivatives (C₆₀Rn (R═F: n=2 to 36,R═H: n=20, R=Me: n=20, and R═Cl: n=24)) were each obtained by carryingout a structure optimization calculation by means of Gaussian 09 andmaking simulation of the optimized structure using a time-dependentdensity functional theory (TD-DFT). In detail, with respect to theultraviolet visible absorption spectra (UV-vis) of various fullerenederivatives, UV-bis calculation using TD-DFT was performed for theoptimized structure, at a calculation level of B3LYP functional, using,as a basis function, a function form (6−31+G (d, p)) in which apolarization function and a dispersion function are added to a doublebasis set. It can be appreciated from FIG. 11 that, in association withincrease in substitution number, the absorption peak is shifted toward ashorter wavelength, thus causing the absorption in the visible range tobe smaller. Further, it is apparent, from respective shifts ofabsorption spectra of C₆₀H₂₀ and C₆₀Fn with respect to an absorptionspectrum of C₆₀, that this tendency is independent of characteristics(electron-withdrawing property or electron-donating property) of thesubstituents.

FIG. 12 illustrates current-voltage characteristics of the organicphotoelectric conversion section 11G in the present embodiment beforeand after light irradiation. FIG. 13 illustrates ultraviolet visibleabsorption spectra of the organic photoelectric conversion layer 17 thatconstitutes the organic photoelectric conversion section 11G. In theorganic photoelectric conversion section 11G, subphthalocyanine is usedas the organic semiconductor (dye) and C₆₀F₃₆ is used as the fullerenederivative. The organic photoelectric conversion section 11G has aconfiguration in which the organic photoelectric conversion layer 17 isprovided on an ITO layer (lower electrode 15 a) that is provided on aquartz substrate by subjecting the subphthalocyanine and C₆₀F₃₆ tocodeposition using the vacuum deposition equipment, with an AlSiCu layer(upper electrode 18) being further provided. A light source, a filter,and a semiconductor parameter analyzer were used for the organicphotoelectric conversion section 11G to measure a current value beforeand after the light irradiation. As appreciated from FIG. 12, it can beseen that the organic photoelectric conversion section 11G of thepresent embodiment has a photoelectric conversion function, fromobservation of a light current upon the light irradiation. Further, itwas confirmed, from FIG. 13, that the organic photoelectric conversionlayer 17 of the present embodiment has no such an absorption, near 400nm, as seen in a photoelectric conversion layer made ofsubphthalocyanine and C₆₀, and that its spectroscopic shape has a risesimilar to that of the photoelectric conversion layer made only ofsubphthalocyanine. In other words, it can be seen that C₆₀F₃₆ does notinhibit the spectroscopic shape of the subphthalocyanine.

As described above, in the present embodiment, the organic photoelectricconversion layer 17 provided between the lower electrode 15 a and theupper electrode 18 is configured by the organic semiconductor and thefullerene having undergone polysubstituted modification (fullerenederivative). Subjecting the fullerene to the polysubstitutedmodification causes the absorption peak wavelength of the fullerene tobe shifted toward shorter wavelength side, and reduces the interactionbetween fullerenes. This improves the spectroscopic shape of thephotoelectric conversion element using the fullerene, thus enhancing theoptical conversion efficiency of the predetermined wavelength region. Inother words, it is possible to enhance the photoelectric conversionefficiency without deteriorating the spectroscopic shape of the organicphotoelectric conversion layer 17. Thus, the use of the photoelectricconversion element 10 of the present embodiment in the solid-stateimaging device described later makes it possible to enhance the colorreproducibility.

2. Application Examples Application Example 1

FIG. 14 illustrates an overall configuration of the solid-state imagingdevice (solid-state imaging device 1) that uses, as each pixel, thephotoelectric conversion element 10 described in the foregoingembodiment. The solid-state imaging device 1 is a CMOS imaging sensor.The solid-state imaging device 1 has a pixel section 1 a as an imagingregion on the semiconductor substrate 11. Further, the solid-stateimaging device 1 includes, for example, a peripheral circuit section 130configured by a row scanning section 131, a horizontal selection section133, a column scanning section 134, and a system controller 132 in aperipheral region of the pixel section 1 a.

The pixel section 1 a includes, for example, a plurality of unit pixelsP (corresponding to photoelectric conversion elements 10) that arearranged two-dimensionally in matrix. To the unit pixels P, for example,pixel drive lines Lread (specifically, row selection lines and resetcontrol lines) are wired on a pixel-row basis, and vertical signal linesLsig are wired on a pixel-column basis. The pixel drive line Lreadtransmits a drive signal for reading of a signal from the pixel. One endof the pixel drive line Lread is coupled to an output terminalcorresponding to each row in the row scanning section 131.

The row scanning section 131 is configured by a shift register, anaddress decoder, etc. The row scanning section 131 is, for example, apixel drive section that drives the respective pixels P in the pixelsection 1 a on a row-unit basis. Signals outputted from the respectivepixels P in the pixel row selectively scanned by the row scanningsection 131 are supplied to the horizontal selection section 133 via therespective vertical signal lines Lsig. The horizontal selection section133 is configured by an amplifier, a horizontal selection switch, etc.,that are provided for each vertical signal line Lsig.

The column scanning section 134 is configured by a shift register, anaddress decoder, etc. The column scanning section 134 sequentiallydrives the respective horizontal selection switches in the horizontalselection section 133 while scanning the respective horizontal selectionswitches in the horizontal selection section 133. The selective scanningby the column scanning section 134 causes signals of the respectivepixels to be transmitted via the respective vertical signal lines Lsigare sequentially outputted to horizontal signal lines 135, and aretransmitted to the outside of the semiconductor substrate 11 through thehorizontal signal lines 135.

A circuit part configured by the row scanning section 131, thehorizontal selection section 133, the column scanning section 134, andthe horizontal signal lines 135 may be formed directly on the substrate11, or may be arranged in an external control IC. Alternatively, thecircuit part may be formed on another substrate coupled with use of acable, etc.

The system controller 132 receives a clock, data instructing anoperation mode, etc., that are supplied from the outside of thesubstrate 11. The system controller 132 also outputs data such asinternal information of the solid-state imaging device 1. The systemcontroller 132 further includes a timing generator that generatesvarious timing signals, and performs drive control of peripheralcircuits such as the row scanning section 131, the horizontal selectionsection 133, and the column scanning section 134 on the basis of thevarious timing signals generated by the timing generator.

Application Example 2

The above-described solid-state imaging device 1 is applicable to anytype of electronic apparatus having an imaging function, for example, acamera system such as a digital still camera and a video camera, and amobile phone having the imaging function. FIG. 14 illustrates an outlineconfiguration of an electronic apparatus 2 (camera) as an examplethereof. This electronic apparatus 2 may be, for example, a video camerathat is able to photograph a still image or a moving image. Theelectronic apparatus 2 includes, for example, the solid-state imagingdevice 1, an optical system (optical lens) 310, a shutter device 311, adrive section 313 that drives the solid-state imaging device 1 and theshutter device 311, and a signal processing section 312.

The optical system 310 guides image light (incident light) from asubject to the pixel section 1 a in the solid-state imaging device 1.The optical system 310 may be configured by a plurality of opticallenses. The shutter device 311 controls periods of light irradiation andlight shielding with respect to the solid-state imaging device 1. Thedrive section 313 controls a transfer operation of the solid-stateimaging device 1 and a shutter operation of the shutter device 311. Thesignal processing section 312 performs various signal processes on asignal outputted from the solid-state imaging device 1. An image signalDout after the signal process is stored in a storage medium such as amemory, or outputted to a monitor, etc.

Description has been given hereinabove referring to the embodiment;however, content of the disclosure is not limited to the foregoingembodiment and the like, and various modifications may be made. Forexample, in the above-described embodiment, the photoelectric conversionelement (solid-state imaging device) has a configuration in which theorganic photoelectric conversion section 11G that detects green light,and the inorganic photoelectric conversion sections 11B and 11R thatdetect blue light and red light, respectively, are stacked. However, thecontent of the disclosure is not limited to such a structure. In otherwords, red light or blue light may be detected in the organicphotoelectric conversion section, and green light may be detected in theinorganic photoelectric conversion section.

Further, the numbers of these organic and inorganic photoelectricconversion sections, and the ratio therebetween are not limitative. Twoor more organic photoelectric conversion sections may be provided, orcolor signals of a plurality of colors may be obtained only by theorganic photoelectric conversion sections. Furthermore, the organicphotoelectric conversion section and the inorganic photoelectricconversion section are not limited to have a vertically-stackedstructure, and may be arranged side by side along the substrate surface.

Moreover, the foregoing embodiment exemplifies the configuration of thebackside illumination type solid-state imaging device; however, thecontent of the disclosure is also applicable to a solid-state imagingdevice of a front surface illumination type. Further, the solid-stateimaging device (photoelectric conversion element) of the disclosure doesnot necessarily include all of the components described in the foregoingembodiment, and may include any other layer, conversely.

It is to be noted that the effects described herein are merely examplesand are not necessarily limitative; the effects may further includeother effects. It is to be noted that the present disclosure may havethe following configurations.

[1]

A photoelectric conversion element including:a first electrode and a second electrode that are disposed to face eachother; andan organic semiconductor layer that is provided between the firstelectrode and the second electrode, and contains a fullerene derivativemodified by a substituent having an absorbance smaller than that of afullerene in a visible range.

[2]

The photoelectric conversion element according to [1], in which thefullerene derivative is represented by formula (1):

where R denotes, each independently, a hydrogen atom, a halogen atom, alinear, branched or cyclic alkyl group having carbon atoms ranging from1 to 12, a phenyl group, a group having a linear or condensed aromaticcompound, a group having a halide, a partial fluoroalkyl group, aperfluoroalkyl group, a silyl alkyl group, a silyl alkoxy group, an arylsilyl group, an arylsulfanyl group, an alkylsulfanyl group, anarylsulfonyl group, an alkylsulfonyl group, an aryl sulfide group, analkyl sulfide group, an amino group, an alkylamino group, an arylaminogroup, a hydroxy group, an alkoxy group, an acylamino group, an acyloxygroup, a carbonyl group, a carboxy group, a carboxoamido group, acarboalkoxy group, an acyl group, a sulfonyl group, a cyano group, anitro group, a group having a chalcogenide, a phosphine group, aphosphonic group, or a derivative thereof, provided that n is an integerof 2 or more.

[3]

The photoelectric conversion element according to [1] or [2], in whichthe number of the substituent that modifies the fullerene derivativeranges from 2 to 48.

[4]

The photoelectric conversion element according to any one of [1] to [3],in which the organic semiconductor layer includes an organicsemiconductor that absorbs light of a selective wavelength region.

[5]

The photoelectric conversion element according to any one of [1] to [4],in which the organic semiconductor layer has a photoelectric conversionfunction.

[6]

A solid-state imaging device provided with pixels each having one or aplurality of organic photoelectric conversion sections, the organicphotoelectric conversion section including: a first electrode and asecond electrode that are disposed to face each other; and an organicsemiconductor layer that is provided between the first electrode and thesecond electrode, and contains a fullerene derivative modified by asubstituent having an absorbance smaller than that of a fullerene in avisible range.

[7]

The solid-state imaging device according to [6], in which, in each ofthe pixels, the one or plurality of organic photoelectric conversionsections and one or a plurality of inorganic photoelectric conversionsections are stacked, the one or plurality of inorganic photoelectricconversion sections performing photoelectric conversion of a wavelengthregion different from that of the organic photoelectric conversionsection.

[8]

The solid-state imaging device according to [7], in which

the inorganic photoelectric conversion section is formed to be embeddedinside a semiconductor substrate, and

the organic photoelectric conversion section is formed on first surfaceside of the semiconductor substrate.

[9]

The solid-state imaging device according to any one of [6] to [8], inwhich a multi-layer wiring layer is formed on second surface side of thesemiconductor substrate.

[10]

The solid-state imaging device according to any one of [6] to [9], inwhich

the organic photoelectric conversion section performs the photoelectricconversion of green light, and

the inorganic photoelectric conversion section that performs thephotoelectric conversion of blue light and the inorganic photoelectricconversion section that performs the photoelectric conversion of redlight are stacked inside the semiconductor substrate.

[11]

An electronic apparatus with a solid-state imaging device, thesolid-state imaging device being provided with pixels each having one ora plurality of organic photoelectric conversion sections, the organicphotoelectric conversion section including: a first electrode and asecond electrode that are disposed to face each other; and an organicsemiconductor layer that is provided between the first electrode and thesecond electrode, and contains a fullerene derivative modified by asubstituent having an absorbance smaller than that of a fullerene in avisible range.This application is based upon and claims priority from Japanese PatentApplication No. 2015-108832 filed with the Japan Patent Office on May28, 2015, the entire contents of which are hereby incorporated byreference.It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A photoelectric conversion element, comprising: a first electrode; asecond electrode that faces the first electrode; and an organicphotoelectric conversion layer between the first electrode and thesecond electrode, wherein the organic photoelectric conversion layercomprises: a subphthalocyanine; and a fullerene derivative modified by asubstituent having an absorbance smaller than that of a fullerene in avisible range.
 2. The photoelectric conversion element according toclaim 1, wherein the fullerene derivative is represented by formula (1):

where R denotes, each independently, a hydrogen atom, a halogen atom, alinear, branched or cyclic alkyl group having carbon atoms ranging from1 to 12, a phenyl group, a group having a linear or condensed aromaticcompound, a group having a halide, a partial fluoroalkyl group, aperfluoroalkyl group, a silyl alkyl group, a silyl alkoxy group, an arylsilyl group, an arylsulfanyl group, an alkylsulfanyl group, anarylsulfonyl group, an alkylsulfonyl group, an aryl sulfide group, analkyl sulfide group, an amino group, an alkylamino group, an arylaminogroup, a hydroxy group, an alkoxy group, an acylamino group, an acyloxygroup, a carbonyl group, a carboxy group, a carboxoamido group, acarboalkoxy group, an acyl group, a sulfonyl group, a cyano group, anitro group, a group having a chalcogenide, a phosphine group, aphosphonic group, or a derivative thereof, provided that n is an integerof 2 or more.
 3. The photoelectric conversion element according to claim1, wherein a number of the substituent that modifies the fullerenederivative ranges from 2 to
 48. 4. The photoelectric conversion elementaccording to claim 1, wherein the organic photoelectric conversion layerincludes an organic semiconductor configured to absorb light of aselective wavelength region.
 5. The photoelectric conversion elementaccording to claim 1, wherein the organic photoelectric conversion layerhas a photoelectric conversion function.